The y-intercept (where x = 0) of the equation is at -20.
For every 60 the x runs, the y falls by -10. Use rise over run to determine the slope of the equation.
[tex] \frac{-10}{60} = - \frac{1}{6} [/tex]
Slope-intercept form is determined by the following equation:
[tex]y = mx + b[/tex]
m is your slope, and b is your y-intercept.
Plug the slope and y-intercept into the equation.
[tex]y = -\frac{1}{6}x - 20[/tex]